Vegetable Crop Update – A.J. Bussan, Professor, Department of Horticulture, UW-

Madison, Phone: 608-225-6842, E-mail: ajbussan@wisc.edu.

Potatoes: The slight cooling should provide a large benefit to the potato crop, especially the

lower night time temperatures. When low temperatures exceed 70ºF we tend to see decreases in

potato bulking rates that ultimately lead to reductions in the solid content, or specific gravity of

the potatoes.

In addition, as we begin to accumulate days with high low temperatures in excess of 70ºF, we

tend to see changes in sugar content of potatoes as well. During early bulking we tend to see

increases in sugar end defect in processing potatoes. If the warm temperatures occur during late

tuber bulking we tend to see increases in stem end defect. Over the past 2 weeks we have

accumulated more than 8 days with lows greater than 70ºF. Continued warm conditions will

increase the likelihood that stem end defect will be an issue in chipping potatoes.

There have been reports of heat necrosis in several potato varieties in Central Wisconsin as well.

Heat necrosis occurs when cells in the cortical tissues die in response to heat stress. Tubers are

especially sensitive to heat necrosis during tuber initiation or early bulking or when tubers are 1

to 3.5 cm in diameter. Heat stress is caused if soil temperatures exceed 50 to 60ºF for 5

consecutive days. We definitely had soil temperatures in excess of 60ºF as we had 10 days with

low temperatures that were greater than 65ºF from May 15 to June 15.

More specifically, Wisconsin experienced nightly low temperatures greater than 50ºF every night

from May 23 to May 29 and June 8 to June 11. Many fields initiated tubers by May 15 in

Wisconsin. Depending on the potato variety, many fields likely had potato tubers 1 to 3.5 cm in

In This Issue

Impacts of heat on potato production

Heat effects and irrigation demands of vegetable crops

Drought information resources for field crops

Determinate vs. indeterminate potato varieties

Control release N updates

Blossom end rot in pepper and tomato

Early blight and late blight forecasting and disease updates

Cucurbit powdery and downy mildew update

Potato blackleg, onion fungicides

Potato leafhopper control

Colorado Potato Beetle update

Managing onion thrips, insects in cole crops and sweet corn

European corn borer update

Calendar of Events

July 13 – UW-

Rhinelander Ag Research

Station, Potato Tour,

10AM-2PM

July 24 – UW-Hancock Ag

Research Station, Field

Day, 12:30-4:00PM

August 2 – UW-Langlade

County Ag Res Station

Field Day Antigo, 1:00PM

Vegetable Crop Update

A newsletter for commercial potato and vegetable growers prepared by the

University of Wisconsin-Madison vegetable research and extension specialists

No. 16 – July 11, 2012

diameter at one or the other or both dates. Scout tubers to determine if heat necrosis is an issue to

prepare for decisions with regard to marketing or sorting potatoes.

Fresh Market Vegetables: Most of Southern Wisconsin is in severe drought. At the Arlington

Ag Research Station, total precipitation has been 0.58 inches since May 1 with no appreciable

precipitation in 3 weeks. The lack of precipitation and drought conditions are most prevalent in

the Southern half of Wisconsin. Limited precipitation has fallen south of an imaginary line

running from near La Crosse to Green Bay, although this is variable across the state.

Many farmers are irrigating vegetable crops. Application of irrigation water after skins are

cracked due to drought effects on vegetables will lead to rapid growth and rupturing of the fruit

leading to visible growth cracks. Inconsistent irrigation and drought conditions can also limit the

movement of calcium to the fruit. This ultimately leads to weakened cell walls that ultimately

rupture and then can become infected by bacteria. This is commonly seen as blossom end rot.

Many folks may treat crops with foliar calcium fertilizers to overcome this affect. The reality is,

the best way to manage fruit cracking, blossom end rot, and tapered fruit is to irrigate evenly and

adequately (see Matt Ruark’s article on blossom end rot in this newsletter).

So how much water do the crops need? Right now, crops are using about 1” of water every 3 to

4 days depending on ET. Therefore, to meet crop needs growers need to apply 27,000 to 30,000

gallons of water every 4 days to meet crop water demands. What is the best way to recover? If

your crops are on medium to fine textured soil (silt loam), apply an inch of water (27,000

gallons/acre) over the course of 1 to 2 days. After 48 hours, apply another inch of water within a

1 to 2 day period. Once soil moisture is recovered then apply 1” of water per acre every 4 days.

Many farms may have limited water pumping capacity. In the current season, irrigation will need

to be prioritized to crops with the highest value and shallowest rooting depths first. At this point,

onion, tomato and pepper crops should be prioritized for irrigation. Melon, sweet corn,

winter squash and pumpkin should follow in priority in order listed.

Irrigated acres: Current crop prices are reflecting large potential shortages in grains and forage

crops. Given the current growing season, soybean or field corn could be planted on early

Combined with the lack of precipitation has

been very warm temperatures. Daily high

temperatures have exceeded 85ºF with clear

skies and low humidity every day for the past 3

weeks. Water use for the past month has been

estimated at 7-10” with potential ET of 0.25 to

0.30” every day for the past 3 weeks. Vegetable

crops with rooting depth of 2-3’ including

tomato, pepper, melon, summer squash will be

under severe drought stress without irrigation.

The result of this stress includes tapering of fruit

from the stem to the bud as seen in the image on

left. Symptoms on other crops include fewer

fruit, smaller harvested crops, and cracked skins.

harvested vegetable crops under irrigation or in areas of Northern Wisconsin with adequate

moisture (although shorter growing seasons my limit productivity).

The University of Wisconsin - Team Grains have produced resources to guide mid to late

summer planting of soybean and field corn.

Field Corn: Comments from Joe Lauer regarding double cropping field corn. ‘Double-cropping

corn under irrigation after wheat or peas could work well. In most years, I don’t think we would

have enough GDUs to grow corn to the point of regular silage. This year we might.

So the best option is to plant a long-season corn hybrid and try to maximize quality at flowering.

http://corn.agronomy.wisc.edu/AA/pdfs/A042.pdf (Figure 1)

http://corn.agronomy.wisc.edu/AA/pdfs/A057.pdf

http://corn.agronomy.wisc.edu/Research/03DOP/Late2006.pdf

http://corn.agronomy.wisc.edu/Research/03DOP/Late2005.pdf

Soybean: Shawn Conley felt soybeans planted under irrigation by mid July could produce 20+

bushels. He indicated seed might also be available for late planted crops making this a value

proposition give current crop values. He provided the following link:

http://soybean.uwex.edu/documents/DoubleCropSoybean.pdf

Also recognize that crop residues, waste materials, or by-passed crops might have substantial

feed value relative to many years. If crops have been by-passed and no pesticide residues are

present on the crop that cannot be fed to livestock, contact local extension to facilitate potential

harvest of crops for feed.

Matt Ruark, Assistant Professor of Soil Science, UW-Madison, Department of Soil Science,

158 Soil Science Building, Phone: 608-263-2889, Email: mdruark@wisc.edu.

Ruark Extension Web site: http://www.soils.wisc.edu/extension/

Ruark Lab Web site: http://www.soils.wisc.edu/~ruark/

Determinate vs. Indeterminate Varieties and Characteristics in Potato (written with A.J.

Bussan, UW-Horticulture): Two weeks ago we provided an alternate nitrogen (N)

management plan for indeterminate potato varieties based on petiole nitrate tests and potential

harvest date. Questions have arisen related to how we are defining determinant and indeterminate

growth for potato and which potato varieties are in each category. A common distinction is

related to vine growth. For determinant varieties, vine growth ends at flowering, while

indeterminate varieties have a slowing of vine growth. Supply of N to indeterminate varieties at

flowering will promote additional vine growth and delays vine senescence. Adequate supply of

N well into the growing season will benefit indeterminate varieties, as tuber bulking can continue

to occur while vines are green. This is also why adequate N early in the season for determinate

varieties is so important. Rescue applications of N are not as beneficial because the tuber yield

has already been established at the time of flowering. Some potato varieties have indeterminate

growth habit, but only bulk for a given period of time through the growing season and therefore

behave like determinate potatoes. For example, Russet Norkotah will respond to supplemental

nitrogen fertilizer after flowering, but the vines typically senesce and the crop stops bulking prior

to September.

Table 1. List of indeterminate and determinate potato varieties.

Indeterminate Indeterminate, but behaves like a

determinateƚ

Determinate

Russet Burbank Russet Norkota Yukon Gold

Snowden Gold Rush Norland

Bancock Russet Superior ƚ From a nitrogen management perspective, these varieties will respond to late-season N, as they are indeterminate,

but bulking ends much earlier in the season.

Split-pivot trials comparing polymer coated urea and conventional fertilizer (written by

Matt Ruark and Mack Naber, Associate Research Specialist: We are currently evaluating

the performance of a controlled-release nitrogen (N) product on potato at the commercial field

scale. Previous years’ plot research has shown a potential benefit of using controlled-release

products, but inconsistent results at the field level have been noted. In addition, there is evidence

that petiole nitrate concentrations will need to be interpreted differently if using controlled-

release N, or more specifically, polymer-coated urea (PCU). The PCU product being evaluated is

ESN® (produced by Agrium Advanced Technologies).

A trial was conducted on Russet Burbank where half of a pivot received PCU as the primary N

source and the other half received conventional applications. Both halves received 20 lb-N/ac in

starter (April 13) and 77 lb-N/ac as 32% UAN (May 9). The PCU half also received 132 lb-N/ac

as ESN® and 46 lb-N/ac as urea on May 9. The conventional fertilizer half pivot received 58 lb-

N/ac on May 31 as a custom liquid (29% N).

Petiole samples were collected 30 days after emergence (DAE) (June 7). At this point in time,

the PCU half had received 275 lb-N/ac (all of the planned fertilizer) and the conventional had

received 155 lb-N/ac. Petiole nitrate concentrations averaged 2.23% in the PCU half and 2.19%

in the conventional half. Both of half pivots were within the optimal range for 30 DAE (2.0 to

2.3%). At this point in the growing season, the ESN® appeared to be supplying N in a similar

manner to the lower rate of conventional fertilizer.

Petiole samples were also collected 45 days after emergence (June 22). The conventional half

pivot received another 30 lb-N/ac on June 15 as a custom liquid (29% N); a total of 185 lb-N/ac

was applied to the conventional half and 275 lb-N/ac was applied on the PCU half). The petiole

nitrate concentrations for PCU and conventional were both 1.5%, which would still be in the

optimum range (40 DAE: 1.7-2.2%, 50 DAE: 1.2-1.6%). So, by 45 DAE, the PCU has

maintained a similar N supply to the potato as split applications of conventional fertilizer.

Previous years’ results have indicated that petiole nitrate concentrations may be lower than the

optimum range when using PCU because of the low, yet consistent N supply by the product.

However, with this year’s growing conditions, it appears that the PCU has maintained petiole

concentrations in the optimum range. It is important to note that previous studies have focused

on using PCU as the sole N source, while the 2012 trial has only 50% of the N applied as ESN®.

Petioles will continue to be monitored at 60 and 75 DAE to see if the trend continues. With the

high temperatures, we will want to know if the PCU is continuing its release rate at a desirable

pace.

Blossom end rot in tomato and pepper (Matt Ruark): At a field day on Monday evening,

growers brought several peppers that had blossom end rot. I asked the crowd how many of them

were experiencing the same thing in their fields and about half of the audience raised their hand.

Blossom end rot is a common physiological symptom that destroys fruit quality in tomato and

pepper. A thorough description of symptoms in tomato can be found here:

http://hort.uwex.edu/sites/default/files/Blossom%20End%20Rot.pdf

Blossom end rot is associated with calcium (Ca) deficiency in the fruit. There are two

mechanisms that will cause this, lack of Ca being taken up by the plant or lack of movement

from Ca in leaf tissue to fruit. Lack of plant uptake can be caused by low soil test calcium in the

soil, but this is unlikely for most soils in WI. Other things that can reduce Ca uptake are lack of

root exploration in the soil (low root density) or lack of water movement to root (essentially

anything that would prevent Ca from getting into the root. However, if using drip irrigation it

will not likely be low Ca uptake from the soil. The blossom end rot occurring among fresh

market growers in eastern WI is likely caused by Ca not moving from leaf tissue to the fruit.

On Left: Blossom End Rot of Pepper. Photo

taken by M. D. Ruark, Pardeeville, 7/9/12.

Standard drip irrigation scheduling every other day, or

even once a day, may not have been sufficient to

prevent water stress during fruit development.

Calcium is notoriously difficult to translocate in

within the plant if water stress occurs. If the hot

temperatures return without rainfall, it will be

beneficial to supply water several times a day. But do

not flood the soil, or to keep the soil saturated, but

simply prevent the soil from drying out and causing

water stress in the plant. The goal is not to over-

irrigate, but to more efficiently irrigate.

Vegetable Disease Update – Amanda J. Gevens, Assistant Professor & Extension Vegetable

Plant Pathologist, UW-Madison, Dept. of Plant Pathology, 608-890-3072 (office), Email:

gevens@wisc.edu.

Vegetable Pathology Webpage: http://www.plantpath.wisc.edu/wivegdis/

Current P-Day (Early Blight) and Severity Value (Late Blight) Accumulations

Location Planted 50%

Emergence

P-Day

Cumulative

DSV

Cumulative

Calculation

Date

Antigo Area Early 5/1 5/30 276 14 7/9

Mid 5/10 6/6 238 14 7/9

Late 6/1 6/16 171 14 7/9

Grand Marsh

Area

Early 4/3 5/8 419 13 7/9

Mid 4/15 5/16 372 13 7/9

Late 4/30 NA 316 12 7/9

Hancock

Area

Early 4/1 5/1 476 15 7/9

Mid 4/15 5/10 418 9 7/9

Late 5/1 5/17 375 9 7/9

Plover Area Early 4/3 5/17 433 17 7/9

Mid 4/19 5/18 368 17 7/9

Late 5/1 5/27 305 13 7/9

P-Days and Early Blight: All plantings of potatoes in Central WI have P-Day values exceeding

the threshold of 300 of this time. Early and mid-plantings in the Antigo area are approaching the

threshold of 300. Fungicides for early blight control should be applied in Southern and Central

Wisconsin on all susceptible cultivars of potato at this time. An accumulation of 300 P-Day

values indicates a time at which early blight is favored and first infection may occur.

While it has been dry and hot, Alternaria species can take advantage of moist microclimate

effects of a closed potato canopy. Maintenance of irrigation and fertility for healthy plants

further supports early blight control.

DSVs and Late Blight: We continue to have a slow and steady accumulation of DSVs at all

sites. Earlier plantings in the Plover and Hancock areas are approaching 18 DSVs. An

accumulated DSV of 18 indicates time to initiate fungicide applications for late blight control.

While it has been hot and dry, overhead irrigation coupled with microclimate effects of a closed

canopy and cooler nights may promote prolonged periods of leaf wetness, favoring the

promotion of late blight if the pathogen is present.

A

B

C A B C

A

C

There are no reports of late blight in Wisconsin at this time. This past week there were a few

new late blight reports from MA (tomato), NC (tomato), and ME (tomato and potato, first report

for 2012 production season). To date this production year, late blight has been reported in CA,

CT, FL, MA, ME, NC, NJ, NY, PA, and VA. The website: http://www.usablight.org/ indicates

location of positive reports of late blight in the U.S. and provides further information on disease

characteristics and management.

Cucurbits: Cucurbits have been relatively disease-free this season so far, with the greatest

challenge to the crop being delivery of adequate irrigation. Denser plant canopies and cooler

nights may begin to promote disease in cucurbits. Fields were experiencing bacterial wilt over

the past few weeks.

Cucurbit Powdery mildew: Some reports of early symptoms of powdery mildew have come

from the west side of the state, but I have not seen any in fields I have visited myself. In most

years, cucurbits can tolerate some powdery mildew without need for fungicides. However, when

powdery mildew comes early, some cucurbits, particularly pumpkins, may need protection from

a fungicide. The use of fungicides for controlling this disease may be necessary to maintain fruit

quality, quantity, and storability if disease level becomes high and you’re raising a susceptible

variety. While there is good varietal resistance in cucumber and watermelon, many pumpkin and

squash varieties are susceptible to powdery mildew.

The timing of fungicide control measures is important, as some of the registered materials have

reduced efficacy if applied after infection is well established. Among conventional fungicides

labeled for squash and pumpkin powdery mildew, the following list includes those with good

performance: Nova/Rally (myclobutanil), Procure (triflumizol), Pristine (pyraclostrobin +

boscalid), Cabrio (pyraclostrobin), Topsin (thiophanate methyl), and Sovran (kresoxim methyl).

It is recommended that the above-listed materials be tank-mixed and alternated with broad

spectrum fungicides such as mancozeb or chlorothalonil to limit the development of pathogen

resistance and to provide a fungicide program with a broad disease management scope. In

organic production, there are products with some efficacy against powdery mildew: oils,

bicarbonates, sulfur, and copper.

Powdery mildew on cucurbit leaves (2 pictures on left) and spores of the powdery mildew

pathogen (on right). Spores can be wind dispersed.

Cucurbit Downy Mildew: has not been identified in Wisconsin at this time in commercial fields,

home gardens, or our sentinel monitoring plots. Several states have reported cucurbit downy

mildew this season across a wide range of cucurbit hosts in AL, DE, FL, GA, MD, NC, NJ, OH,

PA, SC, and VA. The newest reports within the past 7 days have been primarily on

cucumber with closest detects in MI and Ontario Canada. I will be keeping tabs on disease

reports in the region and will provide updates in this newsletter. No forecasted risk of movement

of spores from southern and eastern states to Wisconsin at this time. Disease forecaster, Tom

Keever of North Carolina State University reports, “there is low risk for cucurbits near the

Michigan source.” The website: http://cdm.ipmpipe.org/ offers up to date reports of cucurbit

downy mildew and disease forecasting information.

Blackleg is promoted by cool, wet conditions at planting and high temperatures after emergence.

The blackleg pathogen is in the soil wherever potatoes are grown. Levels of infection are

dependent upon seed-handling/cutting techniques, soil moisture and temperature at planting and

emergence, cultivar susceptibility, severity of infection of seed, and potentially, amount of

bacteria in irrigation water, cull piles, or other external sources. Sanitation and disinfesting of

potato cutting equipment and proper handling reduces spread and aids in control of the pathogen.

Treating seed to prevent seed piece decay by fungi can also contribute to blackleg control. Since

the pathogen does well in cool, wet soils, avoid planting in overly wet soil. Crop rotation away

from potato for 2-3 years will help control this disease as the bacterium causing blackleg does

not survive well outside of the potato. While seedborne or vascular black leg cannot be reversed

with applications of fungicides, spread of the bacterial pathogen from infected to healthy plants

and aerial stem rot may be managed in the field with fungicide tank-mixes which contain copper.

Most often, conditions which favor plant to plant spread include high winds and driving rains.

While we have not had such rainy conditions, we have had wind and overhead irrigation which

may promote this condition.

This year, almost all of the black leg I have seen appears to have come from the seed, as

blackening of the vascular system is evident in the lowest of stem sections just below the soil

line. In some cases, no blackening is evident externally, but wilted, necrotic plants exhibited

blackened, slimy vascular systems when stems were cut open.

Field control of aerial stem rot is challenging. Copper containing fungicides such as Kocide can

provide some control of aerial stem rot, and can aid in managing bacterial infection after the crop

has suffered hail damage. However, note that results of these approaches have had varied

success throughout the U.S. In recent work by Dr. Dennis Johnson of Washington State

University, the famoxadone+cymoxanil (Tanos) plus mancozeb tank-mix alternated with

Potato blackleg: is caused by Pectobacterium

carotovorum, formerly Erwinia carotovora.

Symptoms of blackleg were observed on several

potato varieties throughout the state this past week.

Infection of seed with blackleg can result in various

symptoms including poor emergence, chlorosis,

wilting, tuber and stem rot, and darkened or black

slimy stems, and death. Blackleg inoculum can

come from infected seed, infested soil, infested

irrigation water, and by insects.

mancozeb+copper hydroxide (ie: Kocide) was an effective chemical tool in reducing aerial stem

rot in potato. Irrigation management to reduce excess water also greatly enhanced control of

aerial stem rot. Copper hydroxide applications alone did not have as effective of control as

Tanos+copper hydroxide. As Tanos is also an excellent late blight control material, its use as we

approach DSVs of 18 at this time offers an appropriate and effective program for control of both

diseases.

Preparing for onion disease control: I have seen few diseases in onions so far this season. I

have seen some thrips silvering, drought stress, and what seems to be heat damage or sunburn

(bleaching/silvering). However, growers are planning ahead for what may come if weather

trends should change. I have provided an overview here of common diseases and fungicides for

Wisconsin onion. Common onion diseases include Botrytis leaf blight and Botrytis neck rot

caused by Botrytis squamosa and B. allii, purple blotch caused by Alternaria porri, downy

mildew caused by Peronospora destructor, and bacterial diseases such as Xanthomonas leaf

blight (Xanthomonas axonopodis pv. allii) and soft rot (Erwinia or Pectobacterium carotovora)

(Fig.1). Production techniques to avoid mechanical and insect damage in the onion crop

contribute to disease management.

There are currently over 50 fungicides registered for use on onions in Wisconsin and selection of

appropriate materials can be confusing (http://www.plantpath.wisc.edu/wivegdis/

Go to: ‘Slide Sets’: ‘Fungicides’ and ‘Fact Sheets’ for more info). Broad spectrum protectant

fungicides with good disease control are chlorothalonil (for Botrytis leaf blight, purple blotch)

and mancozeb (for downy mildew). Disease control is enhanced when applications of

protectants are alternated with applications of materials such as the strobilurins (ie: Quadris,

Cabrio, Reason, Pristine), Scala, Rovral, Switch, and Omega (in work from Dr. Mary Hausbeck,

Michigan State University). Weekly applications of mancozeb have been shown to provide

protection against downy mildew when spray coverage is good and applications begin before

disease appears. Pristine, Ridomil MZ, Quadris Top, and Inspire Super are also good downy

mildew materials and can be used in alternation with mancozeb (Hausbeck). Copper-containing

materials (ie: Kocide, Champ) are the only true bactericides for limiting diseases such as soft rot

and Xanthomonas leaf blight. Coppers must be applied with good coverage and before disease

appears to be most effective. Non-ionic surfactants can aid in improving coverage. Please note

that Valent has removed onion from the Presidio (fluopicolide) label for this production season.

For further information on any fungicides that may be mentioned in this newsletter, please see

the 2012 Commercial Vegetable Production in Wisconsin Guide A3422. An online pdf can be

found at the link below or a hard copy can be ordered through the UWEX Learning Store.

http://learningstore.uwex.edu/assets/pdfs/A3422.PDF

Figure 1. Symptoms and signs of

common onion diseases in

Wisconsin. Left, downy mildew,

note gray pathogen sporulation;

Right, bacterial soft rot, rot has

spread from neck into onion bulb.

Vegetable Insect Update – Russell L. Groves, Associate Professor and Applied Insect

Ecologist, UW-Madison, Department of Entomology, 608-262-3229 (office), (608) 698-2434

(cell), or e-mail: groves@entomology.wisc.edu.

Vegetable Entomology Webpage: http://www.entomology.wisc.edu/vegento/index.html

Potato leafhopper – Potato leafhoppers populations continue to persist

in many crops, especially those which have not received an at-plant

neonicotinoid in-furrow or seed treatment. Untreated potato at the

Arlington Agricultural Experiment Station have sweep net counts now

exceeding 12.5 adults / sweep and at the Hancock Agricultural

Experiment Station, populations are averaging 7 adults / sweep in our

untreated control plots. The adult potato leafhoppers are small (1/8

inch) wedge-shaped, bright green insects that inject a toxic saliva that

causes injury to many plants. Leafhopper feeding will cause leaf edges

to curl and turn yellow, and leaves will eventually brown and die. This

“hopperburn” is most serious on potatoes, dry beans, and snap beans.

Fields must continue to be scouted on a weekly basis to monitor for this pest and decisions made

to treat to avoid significant yield and quality losses. The potato leafhoppers are best sampled

with a sweep net. For potatoes, take 25 sweeps with a sweep net per sample site, and carefully

turn over 25 leaves per sample site. Select leaves from the middle portion of the plant. Use at

least 10 sample sites per 100 acres. Control measures are recommended when a field averages

one to two adult leafhoppers per sweep and there are more than 15 nymphs per 25 leaves, or if

there are three or more adult leafhoppers per sweep and nymphs are present. For snap beans, take

25 sweeps per sample site with at least 10 sample sites per 100 acres scattered throughout the

field. Nymphs are less mobile and are best scouted by leaf samples. Carefully turn over 25 leaves

per sample site and count nymphs. Select leaves from the middle of the plant and use at least 10

sample sites per 100 acres. If counts exceed one leafhopper per sweep and one nymph per 10

leaves, then control measures are recommended. Consult the Vegetable Entomology webpage for

more details on selected methods of insecticidal control to limit potato leafhopper

(http://labs.russell.wisc.edu/vegento/files/2012/05/A3422.pdf).

Colorado Potato Beetle - Emergence of the 2nd

generation of Colorado potato beetle (CPB)

continues in central Wisconsin with egg deposition beginning and the appearance of early larvae

will soon follow. We can expect to see adult emergence from the soil and egg laying for the next

10-14 days. In northern Wisconsin, the emergence of the 2nd

will begin in another 10-12 days,

depending upon prevailing weather conditions. Recall, it is necessary to avoid the consecutive

use of a single product, or multiple products with these similar MoA’s. The Insecticide

Resistance Action Committee (IRAC) has developed and updates a Mode of Action (MoA)

classification system with a guide to the selection of insecticides or acaricides (http://www.irac-

online.org). As stated in past newsletters, do not reduce or increase rates from manufacturer

recommendations as this can hasten resistance development. Use products at their full,

recommended doses. Reduced (sub-lethal) doses quickly select populations with average levels

of tolerance, whereas doses that are too high may impose excessive selection pressures.

Depending upon the sequence of materials and associated chemical mode-of-action class used

for early-season CPB control, adequate control of the 2nd

generation can be achieved with the

Two potato leafhopper

nymphs on the undersurface

of a leaf

newer registrations containing rynaxypyr (e.g. Coragen) and chlorantraniliprole (e.g. Voliam

Xpress). If no Class 4A compounds (neonicotinoids) were used in early season CPB control,

several foliar registrations offer excellent protection of the multiple lifestages of this insect.

Onion Thrips – Populations of onion thrips

continue to increase at several locations given

the lack of moisture and warm conditions.

Weather over much of southern and central

Wisconsin in the past 3 weeks, coupled with

very warm nighttime temperatures, continue

to increase the risk of rapid population

growth. Thrips are very small, slender

insects that are best seen with a hand lens. A

very distinctive characteristic of thrips are

two pairs of wings that are fringed with long

hairs. Adults are pale yellow to light brown in color. The immature stages have the same body

shape as adults but are lighter in color and are wingless. The onion thrips has a very extensive

range of hosts, including cereals, selected broadleaved crops (e.g. cabbage), and onions. They

also can be a problem on garlic and chive, but generally are not as serious a pest as they are on

onion. The current high populations of thrips will directly reduce both yield and storage quality

of onions. Thrips have a rasping-sucking mouthpart and feed by rasping the surface of the leaves

and sucking up the plant fluid. They feed within the leaf neck in onions and in the protected

inner leaves near the bulb. When population levels are high, thrips can also be found feeding on

exposed leaf surfaces. Both adults and nymphs cause damage. When foliage is severely

damaged, the entire field takes on a silvery appearance and the severe scarring also creates an

entry point for foliar leaf diseases. As noted previously, success in managing season-long

populations of onion thrips relies almost exclusively on the use of insecticides. Proposed

sequences of insecticides used to manage onion thrips are in Table 1.

Table 1. Sequence of insecticides to apply for onion thrips control in Wisconsin onion fields. Two

applications of each product should be considered and timing should be based on an appropriate

action threshold.

Application # Product Action threshold/ Timing of spray to consider

1 Movento 1 thrips larvae per leaf

2 Movento 7 to 10 days after 1st Movento spray

1

3 Agri-Mek 1 thrips larvae per leaf

4 Agri-Mek 1 thrips larvae per leaf

5 Radiant 3 thrips larvae per leaf

6 Radiant 3 thrips larvae per leaf

7 Lannate 1 thrips larva per leaf

8 Lannate 1 thrips larva per leaf 1 If the thrips population is reduced to a low level (e.g., below 1 thrips per leaf) after the first Movento spray and

does not reach threshold again until 3 weeks later, consider avoiding another application of Movento. If this

scenario occurs, the second application of Movento would likely be used against the next generation of thrips.

Based on insecticide resistance management principles, such a case should be avoided if possible. The

recommendation would be to continue the sequence with the next product, which would be Agri-Mek or Radiant.

Lifestages of the onion thrips (egg, 1st instar, 2nd instar,

prepupa, pupa, and male and female adult).

Cole Crops – Populations of imported cabbageworm (ICW) and diamondback moth (DBM)

have increased sharply over the past 2 weeks at many locations in central and southern

Wisconsin. Larvae of the ICW feed on the first formed outer leaves of their host plants, which

often appear riddled with irregularly shaped holes. As the caterpillars become mature, they feed

in the center of the plant. The last instar larva does the most feeding damage. Initial damage

from the DBM results in small incomplete holes caused by young larvae and larger complete

holes caused by mature larvae. The entire plant may become riddled with holes under moderate

to heavy populations. Larvae also feed in the developing heads of cabbage, causing deformed

heads and encouraging soft rots. However, because of their small size, relative to the cabbage

looper (CL) and ICW, it takes approximately 20 DBM larvae to defoliate as much cabbage as 1

looper, or 2 ICW larvae. Flights of the CL have been detected in southern portions of the state

ovber the last 4 weeks of the summer with the warm weather.

Similarly, scouting for thrips in cabbage can be integrated with scouting for larvae (worms). A

total of 40-50 plants should be examined weekly with a focus on the field perimeters where

thrips infestations often first appear. Both adult and immature thrips are frequently observed on

the undersides of leaves or within the developing head. They are often difficult to find, making

it important to also look for signs of feeding which can appear as small tan or golden-colored

blisters on infested leaves. During scouting, gently turn wrapper leaves over and examine the

underside for mobile thrips stages; both adults and immatures.

Sweet Corn (WCR) – Populations of western corn rootworm (WCR) beetles have increased

sharply over the past week as temperatures are conducive for flights at many locations in central

and southern Wisconsin. The WCR historically has been a pest in later July when they emerge

and attack susceptible corn. Over the past several days at the Arlington Agricultural experiment

Station, newly established, V-5 stage sweet corn plots have been significantly affected with

rootworm beetles silvering many young plants. According to degree day (DD) model

assessments for this insect, approximately 50% of the adult population could re-emerge in the

south-central and southwestern counties. Adults resulting from the current emergence are

looking for susceptible stages of corn in which to infest and then begin egg laying.

European Corn Borer (ECB) - As daytime high temperatures are anticipated to remain above

average through the remainder of the upcoming week, second generation adult ECB is likely to

be an emerging threat in portions of very western and southern portions of Wisconsin. The

established thresholds for initiation of the 2nd

generation flight occurred at 1,400 DD which has

been surpassed in several southern locations of the state. Adult ECB’s can be expected to appear

in low to moderate numbers across this area of the state in black light traps. The peak of summer

moth activity is projected for 1,733 DD. Here again, silking sweet corn, flowering to pin-pod

snap beans, and peppers with early developing fruit should be closely monitored and black light

trap results for these particular regions should be closely watched as well.

The UW-Agricultural Station in Rhinelander extends a Field Day invitation to all potato

growers, allied partners and friends of our state potato industry.

The UW College of Ag. And Life Sciences has been working since the mid 1940’s at our station,

where potato breeding and variety selection has been the focus. Come and hear presentations

about current developments: Infrastructure, Breeding projects, Variety and Advanced line

progress, Specialty potatoes, National trialing and reports from Extension Specialists and Seed

Certification.

We will have the distinct privilege of welcoming Kate Vandenbosch, the new Dean of the

College of Ag. And Life Sciences, for her first visit to the Rhinelander Station.

This will be a relaxed day in the Beauty of Northern Wisconsin. Delegate your work, jump on

your cycle or just plain get in the truck and show up.

We look forward to seeing you on the 13th

!

Bryan Bowen and staff Where: Rhinelander Agricultural Research Station (Breeding Station)

Directions at this link:

http://ars.wisc.edu/rhinelander/directions.html

When: Friday, July 13, 2012

Time: 9:45am Welcome

10:00am to 12:00 – field tour

Noon – lunch provided by Servco FS

2012

Rhinelander Agricultural Research Station

Potato Field Day, Friday, July 13

Agenda: Breeding and Specialist presentations

9:45am, Welcome to station and review of recent infrastructure projects, CIH, Thanks and

recognition of other venders - Bowen (presented in Willis Storage Bldg)

10:00 load wagons

Speaker Location

10:05 Breeding Program Overview Palta Greenhouses 5-8

10:20 Insect & Disease Update Groves, Gevens N9

(Travel to south fields)

10:40 Irrigation Water Expansion Bowen pond

10:45 Breeding Topics Navarro S9-10

10:55 Student Research Project Kyle Rak S9-10

11:05 Specialty Potatoes Bowen S9-10

(Travel to north fields)

11:20 NFPT and NCPT activities Bussan N1-3

11:30 Advanced Selection Multiplication Navarro, Bowen N1-3

And Maintenance

11:40 Seed Certification Topics Charkowski N1-3

(Travel to Buildings)

12:00pm- 1:15, Lunch Servco-FS Willis Building

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1:30-3:00 SPUDPRO meeting Spudpro Committee TBA